brute-forcing a keygen

brute.js

var fs = require("fs");
var command = ""; 
var realSecret = "Z5ELZYDJ2ZSTXMXCEIQLETFWS25AGZVWOGTEDUEOWB4JFALL5RAQ";
var epochEndTime = 1475280000; // 10/1/2016 0:0:0 GMT
var epochTime = 1476575999 // start here and move backwards - 10/15/2016 23:59:59 GMT
const execSync = require('child_process').execSync;

// We're going backwards in time
while (epochTime > epochEndTime) {
    // javascript time is in ms, so multiply * 1000
	var dateString = date2str(new Date(epochTime * 1000), "yyyy-MM-dd hh:mm:ss");
	command = 'LD_PRELOAD=/usr/lib/i386-linux-gnu/faketime/libfaketime.so.1 FAKETIME="' + dateString + '" ./keygen -g -k 559018485 -o 559018485-mst.key';
	
	code = execSync(command);
	var buf = fs.readFileSync('559018485.key', "utf8");
	var secret = buf.split("secret=")[1];
	if (secret.includes(realSecret)) {
		console.log("we got it!", epochTime, secret);		
		process.exit();
	}
	
    // Just providing some progress to the screen 
    // so we know things are still going 
	if (i % 1000 === 0) {
		console.log(i, dateString);		
	}
	
	epochTime--;
}

function date2str(x, y) {
    var z = {
    M: x.getMonth() + 1,
    d: x.getDate(),
    h: x.getHours(),
    m: x.getMinutes(),
    s: x.getSeconds()
    };
    y = y.replace(/(M+|d+|h+|m+|s+)/g, function(v) {
        return ((v.length > 1 ? "0" : "") + eval('z.' + v.slice(-1))).slice(-2)
    });
    return y.replace(/(y+)/g, function(v) {
        return x.getFullYear().toString().slice(-v.length)
    });
}